Conventionally, an automatic pool cleaner (“APC”) may be considered either “hydraulic” or “electric” depending on the source of energy employed to effect its movement within a pool, spa, or other water-containing vessel. “Electric” cleaners, sometimes also called “robots,” typically use electricity to power motors used to drive wheels or treads to allow the cleaners to move throughout the vessel. Although on-board batteries are sometimes considered to supply electricity to the robots, more likely electricity from mains outside the vessels is conveyed via electrical cords to the robots within the vessels.
“Hydraulic” cleaners, by contrast, connect to external pumps and utilize water flow caused by operation of the pumps to effect their movement within a pool or spa. Some hydraulic cleaners connect to pump outlets; these devices are called “pressure-side” APCs, as pressurized water from pump outlets typically drives the cleaners. Alternatively, hydraulic cleaners may connect to inlets of pumps. These “suction-side” cleaners often include valves and supporting structure designed periodically to interrupt water flow through their bodies to the pumps. Periodic flow interruption creates a “water-hammer” effect, with the resulting energy used to move the APCs within pools.
U.S. Pat. No. 4,742,593 to Kallenbach discloses exemplary valves useful in water-interruption, suction-side hydraulic APCs. A flexible-walled, “diaphragm” valve of the Kallenbach '593 patent may be placed within a chamber of a body of an APC, with the chamber filling with water upon immersion of the APC within a pool. As noted therein:
Expansion of the valve and release for it to reassume its relaxed condition is by the creation of a pressure differential across the valve member walls, i.e., a pressure difference between the chamber and the interior of the valve member. This is created by the suction [of the external pump]. The valve is autonomously opened and closed. Applied suction initially causes the valve to open; but with water flow established, the pressure within [the] valve drops below that of [the] chamber. The valve thus closes. The cycle autonomously repeats.
See Kallenbach '593 at col. 2, 1. 64 to col. 3, 1. 6 (numerals omitted).
U.S. Pat. No. 5,014,382 to Kallenbach illustrates an exemplary suction-side APC in which, for example, a valve of the Kallenbach '593 patent may be positioned. As shown in the Kallenbach '382 patent, the APC includes a flexible disc designed periodically to contact the surface to be cleaned as well as a body and an extension pipe both having a water-flow passage therethrough. Well depicted in the sole FIGURE of the Kallenbach '593 patent is that, when the flexible disc contacts a pool floor or other generally horizontal surface, water flows through the water-flow passage at an angle of approximately forty-five degrees thereto. A flexible hose connected to the end of the extension pipe remote from the disc continues to convey the water toward an inlet of a pump.
Combined with the acutely-angled flow path, the water-hammer effect provided by the interrupt valve tends to lead the APC in the direction of the horizontal vector component of the flow path. The result is that the APC effectively “follows” the hose, decreasing the randomness of movement of the APC along the pool floor and thus inhibiting cleaner of the entire floor. Similarly, by “following” the hose with its movement, the APC may be led into a corner of a pool or behind an obstacle with no automatic means of escape.